This application requests support to initiate a longitudinal study of behavioral precursors of alcoholism in a population of 12-year-old Finnish twin children. Over a five-year period, approximately 6,000 twin children, ascertained from nation-wide birth cohorts, will be assessed, at baseline and biennial follow-up, with self-reports and parental/teacher-ratings. Both parents of all twins will complete questionnaire assessments of their use, tolerance, and dependency on alcohol. From each of four consecutive twin cohorts, two subsamples will be intensively followed-up: 180 twin pairs will be randomly selected, and each random subsample will be supplemented by approximately 70 twin pairs ascertained at elevated risk for the development of alcoholism by baseline screening of their parents. Twins in the two selected subsamples will be rated by classmate peers during in-school exercises that include peer assessments of the twins' closest classroom friends. Parents of random and at-risk subsamples will be interviewed, at local health centers, using relevant sections of Semi- Structured Assessment for Genetics of Alcoholism (SSAGA). At age 14, intensively studied twins will be interviewed with the Adolescent Version of SSAGA. The aims of this research effort are: (i) to evaluate contributions of parental alcoholism and other parental psychopathologies to type and prevalence of behavioral precursors for alcohol abuse observed during mid-childhood and early adolescence; (ii) to assess heterogeneity in pathways to alcoholism by following developmental trajectories of aggressive, anxious, and adaptive behavioral dispositions, modeling genetic and environmental influences on continuity and change over time; (iii) with unique data, from large samples of male/female dizygotic twin pairs, to robustly analyze gene X gender interactions in the expression of alcohol risk; (iv) to test assumptions that the phenotypic covariance of alcohol abuse and temperament reflect common genetic dispositions and shared environmental origins, and explore mediating and moderating effects on that covariance; (v) to assess effects of variation in the timing of psychosexual maturation on onset of alcohol use and the sequential development of abuse; and, (vi) to evaluate influences of parental attitudes and expectations toward alcohol; of parental modeling and parental monitoring; of family structure, support and stress; and of characteristics of peers and residential and school neighborhoods on (twin) children's alcohol expectancies and the onset, development, and familial aggregation of their social drinking patterns. Results will provide a foundation for the continuing study of these twin cohorts as they develop into late adolescence and early adulthood.